The present invention relates to continuous centrifugal casting of metal strands, especially steel.
As it is known, a method of continuous casting of metal, especially steel, in which the liquid metal in the ingot mold is rotated about the axis of the latter, provides, as compared with a continuous casting method in which the liquid metal is not rotated, a considerable improvement as far as the quality of the resulting product is concerned, especially with regard to the cleanliness of the outer skin as well as the inner structure of the casting. The cleanliness of the outer skin is shown, on the one hand, by a surface free of incrustations of slag due to the gathering of such slag at the center of the free surface of the metal in the ingot mold which, under the effect of the rotational movement will assume a concave shape, from the center of which the concentrated slag may easily be removed, and, on the other hand, by the reduction in the first few centimeters of the solidified metal of the number of non-metallic inclusions resulting from the transfer of the latter toward the axis of the cast product. The improvement of the internal structure is characterized especially by the reduction of its central porosity and by suppression of axial macrosegregations, which results are obtained due to the formation of a large equiaxed zone of solidification to the prejudice of a peripheral zone of solidification of the basaltic type which is correspondingly reduced.
Two methods of continuous centrifugal casting of metals are known, that is the continuous centrifugal casting of metal by mechanical means and the continuous centrifugal casting of metal by electromagnet means. These two methods differ from each other mainly by the means utilized in order to rotate the liquid metal in the ingot mold. In the first-mentioned method the centrifugal action is obtained by mechanically rotating the assembly of elements forming the ingot mold itself, whereas in the second method the centrifugal action is obtained by the action of a magnetic field which turns about the axis of the mold and which is usually produced by a stationary multiphase inductor located in the water jacket surrounding the ingot mold. From a technological point of view, the process in which electromagnet means are used for rotating the liquid metal in the ingot mold is preferably to the other method in that it can be carried out by simpler means, due to the absence of any movable mechanical member to assure the rotation of the liquid metal, and furthermore this method may also be used for continuous casting of curved metal strands and for the production of metallic strands of various cross-sections, that is not only round, but also square or similar non-round cross-section. As far as the finished product is concerned, it can be said that, at the present state of development of the two methods, the products respectively obtained from the same are of very similar quality. The two methods have, however, a common disadvantage due to the concentration of non-metallic inclusions in the axial zone of the cast product. These shortcomings of the finished products can be observed after rolling of the products and in particular these internal faults are observed in the interior of the steel tubes obtained during continuous centrifugal casting of the same.